1. Technical Field
This disclosure relates to aircraft flight sensors in general, and in particular, to a system for the in-flight detection of small wing flap deflections that are indicative of failures of the flap structure or flap drive mechanism using existing flap sensors that have measurement errors on the same order of magnitude of the small deflections being detected.
2. Related Art
Flaps are airfoil surfaces moveably coupled to the trailing edge (TE) of the wings of a fixed-wing aircraft by means of powered hinging/lowering drive mechanisms typically located at the opposite ends of each flap. As the flaps are lowered and/or extended relative to the wing during landing, lift and drag are increased to permit slower approach speeds and greater maneuverability. Other types of flaps, referred to as “slats” or “Krueger flaps,” may also be used on the leading edge of the wings of some high-speed jet aircraft.
Certain failures of the structural members or drives of TE flaps of some types of modern aircraft can result in a condition referred to as “freewheeling skew” in which one side of the flap becomes disconnected from the associated flap drive mechanism, thereby allowing the flap to move freely about the hinge point of the flap. Due to the stiffness of the flaps, this creates only small deflections when aerodynamic loads are applied to the flap during flight. However, if this type of failure goes undetected, the flap can become completely disconnected from the aircraft, resulting in a more serious failure. Additionally, this type of failure is usually not obvious when the aircraft is at rest or taxiing on the ground because the disconnected side of the flap will not droop conspicuously, due to the stiffness of the flap and the configuration of the flap-to-aircraft connection structure. Methods and apparatus are therefore needed to detect this type of failure reliably and without adding significant weight or cost to the aircraft.
The problem becomes one of detecting small flap deflections with a light weight system that uses existing, low-accuracy flap sensors that have measurement errors of the same order of magnitude as the small deflections being measured to detect freewheeling skew. Existing solutions include the provision of additional structure, i.e., redundant or multiple load paths, between the flap and the wing. These solutions function by preventing the flap from becoming disconnected from the aircraft, and hence, are relatively heavy and require costly periodic inspections to detect failures. Hence, the multiple load path solution is acceptable only if no other solutions exist, because it adds substantial weight, cost and complexity to the aircraft.
Additionally, for certain other types of flap configurations, a flap skew failure is readily obvious, even when the aircraft is situated on the ground, because the disconnected side of the flap will droop conspicuously, and hence, can be readily detected on a typical pre-flight “walk-around” of an aircraft having this type of flap configuration. However, visual detection during a walk-around is only applicable to certain aircraft having a different type of flap configuration than the ones contemplated herein.
Accordingly, what is needed are systems that are capable of detecting wing flap freewheeling skew failures reliably, inexpensively and without adding significant weight or cost to the aircraft.